Oxidation resistant lubricant compositions



United States Patent OXIDATION RESISTANT LUBRICANT COMPOSITIONS No Drawing Application June 29, 1955 Serial No. 518,917

5 Claims. (Cl. 252- 496) This invention relates to lubricant compositions, and it isaparticularly directed to the provision of compositions of this character which are highly resistant to oxidative.

attack even when employed as a crankcase or other lubricant in internal combustion engines.

The lubricating art has now developed to the point where a large number of oils, both natural and synthetic, are available for many purposes. While these oils vary widely in make-up and in their physical and chemical properties, all, with minor exceptions, have a tendency to become oxidized in the presence of air, especially under the elevated conditions of temperature and pressure encountered in internal combustion engines. This oxidative attack is responsible in part for the formation of the various types of sludges which build up in oils with 'use, and, in the case of oils employed in engines, it is also responsible for the formation of the solid products which deposit out on the piston and cylinder wall surfaces of the engine.

It has also been noted that when oils are oxidized there are formed various acidic and/or peroxidic decomposition products which apparently either engender 'or promote corrosion of metal surfaces coming into contact with the oil. This corrosive attack becomes particularly severe in the case of metals such as the various copperlead, cadmium-silver and cadmium-nickel alloys which are employed in the fabrication of bearings. Further,

as these decomposition products are formed, they lead to aprogressively more rapid oxidation of the remaining portions of the oil, evidently by a species of chain reaction.

Some success in inhibiting oxidation of oils has been obtained by using one or more of a considerable number of different compounds and classes of compounds which have been shown to possess anti-oxidant properties, and particularly good results have been obtained by using in the lubricant composition a minor percentage of a polyhydric aromatic compound. However, while use of such compounds increases the resistance of lubricating oils against oxidative attack, appreciable oxidation of the oil still occurs, particularly under the severe conditions of use which are encountered in internal combustion engines. Accordingly, it would be desirable if means were available whereby oils could be made much more resistant to oxidative attack than has heretofore been possible.

.It is our discovery that an exceptionally high degree of resistance against oxidative attack can be imparted to lubricating oils by incorporating therein a polyhydric aromatic oxidation inhibitor together with a copolymer of a higher alkyl ester of an u,fl-olefinically unsaturated carboxylic acid of from 3 to 8 carbon atoms and an amino lower alkyl ester of such an acid. Surprisingly enough, it has been found that the use in lubricant oils of both these additives imparts to the resulting lubricant composition a resistance to oxidative attackwhich is far superior to that imparted by the polyhydric am matic compound alone. This result is one which is en tirely unexpected and could not be predicted since the copolymers, when used alone, have substantially no antioxidant eifect on the lubricant composition.

The polyhydric aromatic compounds which can be employed in a practice of the present invention are those which contain a total of two or more hydroxy groups attached to carbon atoms of aromatic character in the molecule. Included in the term are such compounds as catechol, resorcinol, hydroquinone, pyrogallol, hydroxyhydroquinone, 1,4-dihydronaphthalene, 2,6-dihydronaphthalene, and 9,10-dihydroanthracene, wherein two or more hydroxy groups are attached to a single phenyl or condensed phenyl nucleus, as well as compounds such as di-fl-naphthol, 2,2-di(p-hydroxyphenyl) propane, 1,4- di(2,3-dihydroxyphenyl) 2,3 dimethylbutane, di(p-hydroxyphenyl) methane and the like, wherein at least one hydroxy group is attached to each of the two or more phenyl or condensed phenyl nuclei present in the molecule. Further, the term also includes those polyhydric derivatives wherein other substituent groups, such as amino, mercapto, alkoxy, aryloxy, thio, alkyl, aryl,

alkaryl, and aralkyl radicals are also present, e.-g., tertiary I butylhydroquinone, ditertiary butylresorcinol, 1,2-dihydroxy-4-phenylbenzene, 5-octyl 1,2 dihydroxynaphthalene, 1,3-dihydroxy-5-catoxybenzene, 1,2-dihydroxythianthrene, 1,Z-dihydroxy-4-aminonaphthalene, and the like.

Preferred polyhydric aromatic oxidation inhibitors in the compositions according to this invention are the dihydric phenylalkyl oxidation inhibitors of from 8 to 24 carbon atoms. Illustrative inhibitors of this type include ethylcatechol, t-butylcatechol, n-octylcatechol, di(p-hydroxyphenyl) methane, 2,2-di(p-hydroxyphenyl) propane, 1,4-di(p-hydroxy-methylphenyl)-2,3-dimethylbutane and the like. The essential common characteristic of these compounds is the two hydroxyl groups either on a single phenylalkyl group or one each on two separate phenyl groups.

As stated above, the copolymers employed in the practice of the present invention are ones of higher alkyl esters of u,B-olefinically unsaturated carboxylic acids and amino lower alkyl esters of such acids. Expressed structurally, said copolymers are those of an ester having the structural formula:

R3 (H) R1-CH=-C0-R3 with an amino alkyl ester having the structural formula:

In said formulae, R is a lower alkylene group (from 1 to 7 carbon atoms); R and R represent hydrogen atoms or methyl groups; R represents a higher alkyl group (8 carbon atoms or more) such as octyl, Z-ethylhexyl, nonyl, decyl, l-ethyloctyl, 1,1-dimethylhexyl, dodecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, cyclopentyl, 4- ethylcyclohexyl, or the various radicals obtained in the polymerization of propene, butene and other alkenes; R and R represent hydrogen atoms of the same or difierent lower alkyl groups. Representative lower alkyl radicals which R and R may represent are methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, isobutyl, amyl, hexyl, cyclopentyl, cyclohexyl and the like.

More specifically, representative copolymers which can be employed in the practice of the present invention are those which can be formed by reacting one or more of the higher alkyl ester compounds given in Table I below with one or more of. the amino lower alkyl ester compounds given in said table.

3 TABLE'I Higher alkyl esters:

2-ethylhexyl acrylate Dodecyl Y acrylate Pentadeeyl acrylate Z-ethylhexyl methacrylate; Decyl methacrylate- 3,6:dimethyldecyl- .methacrylate Dodecyl methacrylate Pentadecyl methacrylate 1,1-dimethyloctyl methacrylatc- Octyl crotonate Dodecyl crotonate- 2-ethylhexyl tiglate Dodecyl tiglate Octadecyl tiglate Octyl angelate. Pentadecyl ,angelate, Octadecyl angelate. Dodecyl hydrosorbate'v Pentadecyl hydrosorbate Amino lower alkyl esters:

acrylates in which the alkyl groups are lower alkyl groups;. accordingly, such copolymrs form a.. more preferred.

group for use in the practice of this invention.

The copolymers of this invention can be prepared by conventional bulk, solution, or emulsion methods, the copolymerization reaction going forward on the applicati'on' of heat or various light rays, and/or in the presence of a polymerization catalyst. Exemplary catalysts which can be employed for this purpose are the organic peroxides (e.g., benzoyl peroxide, acetyl peroxide, ditertiaryamyl peroxide, lauroyl peroxide, etc), hydrogen peroxide, alkali; metal perborates; and persulfates; boron: 1,1,azodicyclohexane., carbonitrflg; alpha, alpha-azodiisobutyronitrile, and-the. like, the preferred catalysts being those. {of the free radical-liberating type,

such as the various peroxy compounds, T l e-polymerizationnormally is conducted at'elevated temperatures, the exact temperature selected depending -rnore particularly onthe reaction initiator--employed.- As -a general rule, temperatures of from about;50 to -1 5 rC. orhigher arev suitable.

Suitable copolymers for use in the present invention can; be obtained by-using from about--.2.to.35% of the amino lower all yl ester compound; and about 98 tO':'65%' of thehigher alkyl. esters If desired, mixedicopolymers can be employed'by reacting two or morefof the :higher alkyl ester; compounds with one-ormore .:of the :amino' lower alkyl esters, or vice 'versa;

The polyhydric aromatic -oxi dation inhibitor; and-co Q escapes g I polymer is present in a minor proportion, sufficient to inhibit-oxidation; Ingeneral, goodresults are obtained when the amount of the polyhydric aromatic oxidation inhibitor employed in the lubricating oil composition ranges from about 0.01 to 5% by weight, although a preferred range is fromflabout 0.05 to 2% by weight. The copolymer ingredient of the composition may comprise from about .0.'5'- to %:Ib'y: weight thereof, and a preferred range is from about 1' to 5% by Weight.

The compounding agents of thisinvention can be used with good'efi'ectin. the case of: any oil oflubricating viscosity'which is subject-to oxidativ'eattack; This oil can be a refined Pennsylvania or other paraflin base oil, a refined naphthenic base-oil, ora synthetic hydrocarbon or nonhydrocarbon oil Oflubricatingviscosity. As synthetic oils thereacanbe mentionedalkylated waxes and similar alkylated hydrocarbons of relatively high molecular weight, hydrogenated polymers of hydrocarbons, and the a condensationproducts of chlorinated-'- alkyl hydrocarbons with aryl compounds. Other suitable oils' are those which are'obtainedby-polymerization' of lower.

molecular weight alkylene oxidessuch' as propylene and/ or ethylene oxide. Still 'otherisynthetic oils are obtained by etherification and/ or esterification of the hydroxy groups in-alkyleneoxide polymers-such as, for example,

theacetateofthe:2 ethylhexanol1initiated polymer of:

propylene oxide.- Anotheriimportant class of synthetic oil's' cornprises the high Lmolecular weight esters as, for: example, di(ethylhexyl): sebacate; The; silicateesters;

such as the tetraalkylorthosilicates and polyalkoxypolysiloxanes,: for example, te'tra(2-ethylhexyl)orthosilicatev and:hexa(2ethylhexyl)disiloxane, and blends thereof c0 stitute still .another important class of synthetic oilsof:

1ubricating.;viscosity. Ifdesired, the ;oil canbe a mixtureuot mineral and syntheticoils;

The-compounded oils of-zthis; invention; may beguti: lized as turbine oils, cable oils, electric switchoils, transformer.oils,.hydr'aulic oils and the like, ,aswell as crankcase and otherlubricants for5automotive; aircraft, diesel and other internal-combustion engines. These oils, in

addition to the. anti-oxidants described above, canalso contain. additional ingredients such as metal salt detergents (e.g.-, polyvalentmetal phenates, sulfonates, thio phosphates,etc;),'pour-point depressants oiliness agents,

extreme-j pressure addition. agents, other: anti-oxidants;

blooming,agents compounds for enhancing. the.,viscosity index ofthevoil, thickening-.agentsand/or metal soaps in grease-forming;proportions or in amounts insuflicient.

to form grease, as in the case of mineral castor machine 1 oils ,or-other compounded, liquid lubricants.

.A-x-convenientmethods-of, measuringlthet resistance of.

oxidation possessed :-by lubricant compositions is by the use-ottheapparatus :and, procedure described 'in Indus triaLandEngineering.Chemistry, vol. 28,, p.. 26' (1936),

wherein the rate ofoxygen absorptionat' constant.pres-- sure ,by. adefiriiteweight. of zoil isregarded as; a measure,

oftheoxidative stability of the. .oil.f According to this procedure, the oil' sample, is. placed in an absorption cell provided .at its. bottom with, a fine-fritted glass filter to disperse the oxygen, stream .whichis circulated through the. system atta constant rate.- Theparti'cularapparatus employedfin. obtaining the data presented in TabIeJII below was made up, offan oxidation or. absorption cell constructed of a large glass tube provided witha head portion having, a connection for introducing oxygen, a-

fittingfor the insertion of ajstirrer, andanannular, space surrounding the tube 'and'communicatory with themterior thereof for the reception; of potassium hydroxide pellets which serve-to remove'water carbon dioxide,

volatile aldehydes and-the like. The oilsample iscontained inthe 'lowerportion of the tube which, during the test, is immersed-in: an :oillbath maintained at 340 F; The oil --is stirred vigorouslylduringithe test and: is;

kfCRtf-lllldfll a pressure of about -1 atmosphere. of pure oxygen.

The time jn zhours-required: for lofl gramspf the oil to absorb 1200 cc. of oxygen is called the induction period.

The data presented in Table II below illustrate the anti-oxidant effect exerted on the base oil (a highly refined, mineral base white oil, which itself has an induction period of substantially hour) by the addition of the recited additives.

TABLE II Anti-oxidant effect of hydroxy aromatic compound+copolymer on white oil 1PL-164 is a product manufactured and sold by E. I. du Pont de Nemours & Company of Wilmington, Delaware.

Analysis of the product discloses it to be a solution in oil of a copolymer of dodecyl methacrylate and diethyl aminoethyl methacrylate in a weight ratio of about 6.5:1. The percentages employed in the table for the PL-164 are, however, on an oil-tree basis.

The above test data demonstrate the remarkable improvement in resistance to oxidation provided by mineral lubricating oil compositions containing the combination of a polyhydric aromatic oxidation inhibitor and copolymer of a higher alkyl ester of an alpha-beta olefinically unsaturated monocarboxylic acid of from 3 to 8 carbon atoms and an amino lower alkyl ester of such an acid in accordance with the invention. Although the polyhydric aromatic oxidation inhibitors alone in the lubricating oil are shown to provide certain amounts of inhibition, usually about 1.0 hour, a surprising increase in the inhibition period up to as high as about 10.0 hours, or ten told, is obtained when the polyhydric aromatic oxidation inhibitor is employed in combination with a representative copolymer of the aforementioned type. Such a result is Wholly unexpected since the copolymer by itself in mineral lubricating oil apparently has no oxidation inhibiting eflfect.

In further illustration of the anti-oxidant efiect obtained in lubricating oil compositions in accordance with this invention, a commonly available synthetic base oil of lubricating viscosity and subject to oxidative attack was employed in the same test as described above. The synthetic oil in this case was hexa(Z-ethylhexoxy) -disiloxane. The test results are presented in Table III which follows:

TABLE HI Anti-oxidant effect of hydraxy aromatic compound and copolymer on synthetic oil 0 1 f d H droxy Aromatic opo ymer erlo y Compound (Hrs.)

0.2 b wt.t-but lcatechol. None 0.7 Ndiiej. i 5% dodecyl methacrylate] 0.0

diethylaminoethyl methacrylate (PL-164) 0.2% by wt. t-buty hnl do 2. 7

1 PL-164 is as described above in Table II.

hibitor is used together with the copolymer of a higher alkyl ester of an alpha-beta olefinically unsaturated monocarboxylic acid of 3 to 8 carbon atoms and an amino lower alkyl ester of such an acid. This is indeed remarkable when it is considered that the copolymer of itself provides no oxidation inhibition to the hexa(Z-ethylhexoxy)disiloxane synthetic lubricating oil.

In the described tests both the representative mineral lubricating oil and the synthetic lubricating oil when employed alone have no apparent resistance to oxidation, and give induction periods of 0.0 hour.

From the above detailed description, it will be apparent that the combination of ingredients herein disclosed give a new composition having new and highly useful properties. It is immaterial for the purpose of the present invention whether the components be separately new or old, since it is the discovery of the combination of ingredients and the unexpected properties obtained thereby which comprise the applicants contribution to the art.

We claim:

1. A lubricating oil composition having improved resistance against oxidation, said composition consisting essentially of a major proportion of a mineral lubricating oil, from about 0.1 to about 5% by weight of an oxidation inhibitor selected from the group consisting of 2,2-di- (p-hydroxyphenyl) propane and t-butylcatechol and from about 0.5 to 10% by weight of a copolymer consisting essentially of dodecyl methacrylate and diethylaminoethyl methacrylate in a weight ratio of about 6.5:1.

2. A lubricating oil composition having improved resistance against oxidation, said composition consisting essentially of a major proportion of a mineral lubricating oil, from about 0.1 to about 5% by weight of 2,2-di(phydroxyphenyl) propane and from about 0.5 to 10% by weight of a copolymer consisting essentially of dodecyl methacrylate and diethylaminoethyl methacrylate in a weight ratio of about 6.5: 1.

3. A lubricating oil composition having improved resistance against oxidation, said composition consisting essentially of a major proportion of a mineral lubricating oil, from about 0.1 to about 5% by weight of t-butylcatechol and from about 0.5 to 10% by weight of a copolymer consisting essentially of dodecyl methacrylate and diethylaminoethyl methacrylate in a Weight ratio of about 6.5: 1.

4. A lubricating oil composition having improved resistance against oxidation, said composition consisting essentially of a major proportion of a normally oxidizable oil of lubricating viscosity selected from the group consisting of mineral lubricating oil and hexa(2-ethylhexoxy)- disiloxane, from about 0.1 to about 5% by weight of an oxidation inhibitor selector from the group consisting of 2,2-di(p-hydroxyphenyl) propane and t-butylcatechol and from about 0.5 to 10% by weight of a copolymer consisting essentially of dodecyl methacrylate and diethylaminoethyl methacrylate in a weight ratio of about 65:1.

5. A lubricating oil composition having improved resistance against oxidation, said composition consisting essentially of a major proportion of hexa(2-ethylhexoxy)- disiloxane, from about 0.1 to about 5% by Weight of t-butylcatechol and from about 0.5 to 10% by weight of a copolymer consisting essentially of dodecyl methacrylate and diethylaminoethyl methacrylate in a weight ratio of about 6.5: 1.

References Cited in the file of this patent UNITED STATES PATENTS Yates Apr. 27, 1948 Catlin Jan. 12, 1954 Catlin Mar. 6, 1956 OTHER REFERENCES Performance of Lubricating Oils, by Zuidema, Reinhold Pub. 00., N. Y. (1952), pages 73-75. 

4. A LUBRICATING OIL COMPOSITION HAVING IMPROVED RESISTANCE AGAINST OXIDATION, SAID COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF A NORMALLY OXIDIZABLE OIL OF LUBRICATING VISCONITY SELECTED FROM THE GROUP CONSISTING OF MINERAL LUBRICATING OIL AND HEXA(2-ETHYLHEXOXY)DISLOXANE, FROM ABOUT 0.1 TO ABOUT 5% BY WEIGHT OF AN OXIDATION INHIBITOR SELECTOR FROM THE GROUP CONSISTING OF 2,2-DI(P-HYDROXYPHENYL) PROPANE AND T-BUTYLCATECHOL AND FROM ABOUT 0.5 TO 10% BY WEIGHT OF A COPOLYMER CONSISTING ESSENTIALLY OF DODECYL METHACRYLATE AND DIETHYLAMINOETHYL METHACRYLATE IN A WEIGHT RATIO OF ABOUT 6.5:1. 